The present invention relates to a formulation for and a method of colorimetric testing for the concentration of cyanuric acid compounds in aqueous solution. The invention has particular application to testing for concentration of such compounds in swimming pool water and the like although the invention is not limited thereto.
As is well known, maintenance of hygienic conditions in swimming pool water and the like requires the maintaining of chlorine or a chlorine releasing compound in the water as a bactericide. It is also known that cyanuric acid compounds stabilize the chlorine or chlorine releasing compounds against excessive loss by volatilization, etc. Further, there is some ground for belief that excessive amounts of a cyanuric acid compound, or the use of certain cyanuric acid compounds, may tend to over-stabilize the chlorine releasing compound and thereby interfere with the desired bactericidal action of the chlorine. There are known and commercially available cyanuric acid compounds which, when present in the pool water within prescribed concentration limits, satisfactorily stabilize the chlorine releasing compound.
For example, potassium dichloro-s-triazinetrione (common name, potassium dichlorocyanurate) and the sodium salt of dichlorocyanurate are known stabilizing compounds. Other chlorinated cyanurics are also employed. These compounds are usually sold in powder or tablet form for use in swimming pools and the like. In aqueous solution, these compounds dissolve and dissociate so that cyanuric acid exists in equilibrium in the solution. As above indicated, it is desirable to maintain the cyanuric acid compound within a concentration range which is high enough to stabilize the chlorine content against excessive losses but not so high as to possibly inhibit its bactericidal action. Experience has shown that 50 parts per million (all parts per million given herein are by weight) of the cyanuric acid compound (as cyanuric acid) is the minimum concentration for chlorine stabilization. The maximum cyanuric acid compound concentration is not more than about 200 parts per million, preferably not more than 100 parts per million (both measured as cyanuric acid). Concentrations above these levels may over-stabilize the chlorine.
It is thus apparent that for proper maintenance of swimming pool water and the like, the ability to easily and quickly determine the concentration of cyanuric acid compounds at low concentration levels (between 50 to 200 ppm) is highly desirable and the present invention is particularly applicable thereto.
Potentiometric and turbidometric methods for determination of cyanuric acid compound concentration in aqueous solution are known. However, it will be appreciated that potentiometric methods require sensitive laboratory equipment and that turbidometric methods are inherently inaccurate and difficult to read. For example, one turbidometric method uses melamine to form a precipitate of a melamine cyanuric acid salt. The quantity of precipitate formed in a sample of given size indicates the concentration of cyanuric acid compounds in the solution. But it is difficult to make an accurate estimation, particularly for an untrained operator. Such methods are too involved for the average swimming pool owner or operator to conveniently use.
Accordingly, it is an object of the present invention to provide a novel formulation which gives an easily readable colorimetric indication of the concentration of cyanuric acid compounds in aqueous solution.
It is another object of the present invention to provide such a novel formulation in the form of a single liquid which requires but dropwise addition to a sample of the aqueous solution.
It is another object of the invention to provide a novel method involving the use of such a formulation which provides a color shade characteristic of the concentration of cyanuric acid in aqueous solution, particularly at low (fifty to two hundred ppm) concentrations and one which is readily discernible to the unaided eye.
It is another object to provide a novel colorimetric test for cyanuric acid compounds which is simple enough to be used by unskilled operators.
It is yet another object of the invention to provide such a formulation which is stable both during storage, so that the formulation has a prolonged shelf life, and during exposure to bright sunlight conditions, such as those which normally prevail at swimming pools and the like.
Other objects and advantages of the invention will become apparent from the following description.